This Blood Test Can Detect Colorectal Cancer in 5 Out of 6 Cases
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“That accuracy rate is close to at-home stool tests used for early detection of colorectal cancer,” says the corresponding author William M. Grady, MD, a gastroenterologist at Fred Hutch Cancer Center in Seattle. The blood-based test could offer an alternative for patients who might decline current screening options, says Dr. Grady.
An additional screening option for colorectal cancer is a good thing, says Sean Langenfeld, MD, a colorectal surgeon at Nebraska Medicine in Omaha, who was not involved in the study.
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“Having a blood-based screening test available will lead to more patients agreeing to undergo screening and hopefully improve screening rates, as they see it as less invasive,” says Langenfeld.
Blood Test Accuracy Measured Against ‘Gold Standard’ Colonoscopy
To compare the accuracy of the blood test to a colonoscopy, the current gold standard for colorectal cancer screening, researchers enrolled nearly 8,000 people between the ages of 45 and 84 years old. Participants were 60 years old on average, and 54 percent were women. Among the participants, 78.5 percent were white, 12 percent were Black, and 7 percent were Asian. About 13 percent identified as Hispanic or Latino. The racial and ethnic makeup of the group aligns with the demographics in the 2020 U.S. Census, according to the authors.
In order to be included in the study, participants could only have an “average risk” for colorectal cancer, which is the intended user group for the blood test. That means they had no family history of colorectal cancer, no personal history of cancer, and no diagnosis of inflammatory bowel disease or large polyps.
A total of 7,861 people met all those criteria and completed a colonoscopy as well as the blood test. Out of 65 participants with colonoscopy-detected colorectal cancer, 54 of them also had a positive result (indicating cancer) with the blood test — meaning that the blood test didn’t detect 11 out of 65 cases. That translates to an accuracy rate of about 83 percent.
The test was better at identifying colorectal cancers, including early stage cancers, but less accurate in detecting advanced precancerous lesions, which can turn into cancer over time.
How Does the Shield Test Measure Up to Currently Available Options?
In addition to the Shield blood test, there are two main at-home tests for colorectal cancer.
- The FIT, which stands for fecal immunochemical test, is about 79 percent accurate in detecting colon cancer. The test comes as a kit, with instructions and materials to safely and hygienically collect a small amount of fecal matter (poop) to be sent to the lab for analysis. It’s recommended that the test be repeated every 1 to 2 years.
- Cologuard (fecal DNA testing) has a 92 percent accuracy rate. It also involves collecting a sample and mailing it off, and the test should be repeated every 3 years.
The accuracy of the Shield blood test in detecting colorectal cancer is very similar to current stool-based tests, including FIT, but somewhat below the sensitivity of fecal DNA testing like Cologuard, says Langenfeld. It had a specificity of 90 percent — meaning this test was not setting off many false alarms, he adds.
The Shield test needs to be repeated every 3 years. If a person gets a positive test result, a colonoscopy is recommended to determine if the test result is a true or false positive.
Blood-Based Screening Technology Is Being Studied in Breast and Lung Cancer
The Shield test detects colorectal cancer signals in the blood from DNA that is shed by tumors, which is called circulating tumor DNA.
Grady says the technology is very promising, and is currently being studied to screen for other types of cancer, including breast cancer and lung cancer.
Who Should Use the Shield Colorectal Cancer Test?
“This test is most appropriate for patients unable or unwilling to undergo colonoscopy — that’s who I would recommend it to. Since it is fast, easy, and noninvasive, it will seem like less of a commitment, and will hopefully lead to people undergoing screening who would have otherwise continued to put it off for the foreseeable future,” says Langenfeld.
That being said, the test wasn’t good at picking up precancerous lesions — it identified them only 13 percent of the time. “I will still recommend screening colonoscopy for most patients, he adds.
Polyps are common, especially in older adults, and most are benign, meaning noncancerous. But sometimes polyps can change into cancer — usually over many years. Another benefit of a colonoscopy is that precancerous polyps can be removed during the procedure, says Langenfeld.
Grady recommends talking with your provider about which option is best for you. Currently, when people are given the option of doing a colorectal cancer screening with a stool-based test or with colonoscopy, nearly half of people elect to do neither, he points out.
Shield Is Seeking FDA Approval and Medicare Coverage
When Do I Need to Start Getting Screened for Colorectal Cancer?
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